There have been disclosed a variety of audio signal output circuits adapted to prevent generation of pop noise that occurs at the time of power-on and power-off of an audio output amplifier.
For example, Japanese Patent Application Laid Open No. 2003-258559 (referred to as Document 1) discloses a circuit having a drive amplifier, a coupling capacitor, and a changeover switch for switching the connection of the coupling capacitor to a speaker or to the ground in response to a mute signal received. As a consequence, the signal-flow path to the speaker is shut down and at the same time the coupling capacitor is rapidly charged or discharged to prevent pop noise from occurring.
Thus, the prior art circuit as disclosed in Document 1 disadvantageously requires many such components as coupling capacitor and changeover switch in a later stage of the audio signal output circuit, in addition to a mute signal generator for controlling the switch, which is a drawback in constructing the circuit in the form of an IC.